This invention relates generally to the packaging of electrical systems and devices into a chassis and, specifically, to an improved modular arrangement of the printed circuit boards therein for enabling simple reconfiguration of input/out (xe2x80x9cI/Oxe2x80x9d) interface types and improved fault tolerance for both electrical and optical I/O signals.
Electronic devices, especially those used in communications systems such as cable head-ends and satellite uplink sites, are typically housed in chassis that are then mounted in vertical racks. In such systems, there is a need to provide I/O connectivity to various sources and destinations outside the device as well as to provide internal connectivity within the device. Furthermore, in devices that perform the function of switching, multiplexing, de-multiplexing, routing or other such similar functions, there is often the need to support multiple interfaces of the same type or of different types. These I/O types may be of either a conducted electrical signal or of an optically carried signal. In order to support multiple I/O interfaces of a variety of types, it has been the practice to divide a chassis into multiple identical slots, where each slot can be configured to support a variety of functions and interface types simply by changing the electronics module that occupies the slot. Each of the modules that contain active circuitry then typically needs to connect signals both to external I/O cables and also internally to other circuitry in the device.
Furthermore, it is desirable that such electronic devices provide high availability of service through fault tolerance and the ability to replace faulty circuitry without interrupting the operation of the device. These goals have typically been met by a) providing redundant circuitry that automatically takes over for circuitry that fails, and b) providing the capability to hot-swap faulty circuitry (that is to replace modules while the device is operational and without interrupting the processing of signals that connect to the device).
To make hot-swapping and cable management non-error prone, it has become common practice to construct these devices such that the circuit modules, which hold active circuitry, are replaceable from the front of a chassis while external I/O cabling is connected to the rear of the chassis. This makes it possible for cables to stay in place while faulty circuitry is replaced and eliminates the possibility of reconnecting cables incorrectly. It also eliminates the down-time that would be caused by the interruption of the flow of the signals on those cables while they are disconnected. Furthermore, it is desirable to provide some means to prevent a circuit module from being incorrectly installed in a slot where it would be connected to an inappropriate I/O type.
Existing devices may be categorized as follows:
a) I/O connection via mid-plane board to parallel connector PCB module;
b) I/O connection via perpendicular connector PCB module;
c) I/O connection via detachable connector faceplate.
FIG. 1 illustrates a device in which the mid-plane approach is employed. A circuit module 102 plugs in and out from the front of a chassis and has at least one right-angle connector along its back edge which mates with a corresponding connector 104 on a mid-plane printed circuit board 106. The mid-plane printed circuit board (xe2x80x9cPCBxe2x80x9d) 106 typically extends across the full height of the chassis. Pairs of connectors 104,108 on opposite sides of the mid-plane PCB 106 are mounted in opposition to each other such that they can share pins that pass through the mid-plane PCB 106 to transmit all or some of the signals of the circuit module 102 directly through the mid-plane PCB 106 to a connector module 110. The connector module 110 then makes the connections to the external world using right angle mounted connectors 112 on its rear edge. There is no direct connection from the circuit module 102 to the connector module 110 in this approach.
The mid-plane approach for providing modular I/O connections has been standardized in IEEE 1101.11, wherein the connector modules are called xe2x80x9cRear Plug-in Unitsxe2x80x9d. U.S. Pat. Nos. 5,010,450, 5,315,488, 5,912,801, and 5,488,541 each describe variations of the mid-plane approach.
A disadvantage of the mid-plane approach is the extreme difficulty of making a blind-mateable fiber-optic I/O connection. If it was even realizable, it would be very complex as a blind-mateable optic I/O connection would require multiple fiber optic connections in the signal path between the active circuit module and the eventual external connector on the rear of the connector module. While U.S. Pat. No. 5,010,450 discloses a fiber-optic connection, the connection is not blind-mateable, but requires the physical removal of the cable from the circuit module before the circuit module can be fully removed.
A further disadvantage is that the thru connections from the active circuitry on the front circuit module to the rear connector module cannot be individually tailored with regard to impedance and other electrical characteristics. Rather, one must xe2x80x9cmake doxe2x80x9d with the characteristics of the mid-plane pass-thru connector which cannot be arbitrarily reconfigured on a slot by slot basis.
A still further disadvantage is that a circuit module may inadvertently be inserted in the wrong slot causing the device to malfunction and possibly even destroying circuitry.
Finally, none of these patents present a solution for redundancy in which an I/O signal from a failed circuit module is automatically routed to a spare (backup) circuit module of the same type. Thus, in the event of a failure on a circuit module, the corresponding I/O will not be processed correctly until the faulty module is replaced.
Perpendicular Connector PCB Module
FIG. 2 illustrates a device in which the perpendicular connector PCB approach is employed. It is characterized by a direct connection between a circuit module 202, which contains active circuitry, and a connector module 210, which tailors the external I/O connectors 212 to a particular I/O type. However, the connector modules 210 are not co-planar with the circuit modules 202. Moreover, each connector module 210 is a fairly complex assembly typically involving at least two PCBs that are perpendicular to the circuit module 202, inter-board connections 214 and multiple stand-offs and spacers (not shown) (see U.S. Pat. No. 5,430,615 for an example). One PCB 216 directly behind the faceplate 218 holds the external I/O connectors 212 and another PCB 220 holds the connector which makes a direct connection to the circuit module 202. An additional board-to-board stacking connector 214 is used to transport signals between the two PCBs within the connector module 210. Two PCBs are typically required because the external I/O connectors 212 are generally thru-hole components and hence their protruding leads prevent another connector from being installed directly opposite on the backside of the PCB. By placing the stacking connector 214 off to the side, connectors can be mounted directly opposite one-another. Occasionally, when the slot density in the chassis is low, this approach can be implemented with one perpendicular PCB. However, the slot-to-slot pitch that can be achieved will thereby be limited, along with the density of the electronics. Furthermore, this approach has a high manufacturing cost.
U.S. Pat. No. 5,430,615 discloses a variation on this approach in that it does not include the inter-circuit module connectivity (i.e. cards in one slot cannot communicate to cards in other slots because there is no interconnect PCB which spans across slots). Furthermore the patent presents no solution for optical fiber signals or redundancy.
U.S. Pat. No. 6,144,561 discloses another variation on this approach in that it employs a full top-to-bottom mid-plane board in the chassis, and it connects each circuit module to its connector module via a dedicated hole in the mid-plane. This hole may present a problem: if the hole is not sufficiently large at initial design to accommodate all future connectors to be used, types or number of I/O signals in future modules may be limited. While this patent discloses a one-for-one redundancy method, it does not disclose any means for the much more efficient 1-for-n redundancy. Moreover, this patent fails to disclose how optical fiber I/O connections are achieved in such a way that would be apparent to one skilled in the art.
Neither patent discloses any method to prevent incorrect installation of a circuit module.
Detachable Connector Faceplate
FIG. 3 illustrates a device in which the detachable connector faceplate approach is employed. Internal connectivity is achieved via a back-plane board 306A or side-plane board 306B, and the external I/O connections are made by a direct connection from the circuit module 302 to pass-thru bulkhead mounted connectors 312 on the rear faceplate. In this approach there is no PCB in the connector module and herein lies the main disadvantage of this approach. Without a PCB, one is limited to special pass-thru connectors that have mating right-angle connectors that can be mounted to the circuit module. This class of connector is very rare and may only be available in the BNC type. D type and others are not generally available in a pass-thru configuration. Thus, this approach cannot easily support a wide variety of external connector types. Furthermore, without a PCB, it is not apparent how the external I/O signals can be routed to redundant back-up circuitry in such a way that the connectivity will be maintained while the active circuit module is replaced.
U.S. Pat. No. 6,283,778 discloses a side-plane version of this approach, with all the disadvantages described above. Additionally, it does not support optical fiber connections and does not prevent the circuit module from being inadvertently inserted in the incorrect slot. And, the rear circuit board (30b) of FIGS. 16 and 17 of U.S. Pat. No. 6,283,778 retracts with the circuit module (30a) as a single unit; thus, there is no printed circuit board that permanently resides at the rear of the chassis.
The present invention provides an internal architecture of a chassis product that is to be mounted in a vertical rack with other electronic chassis. The architecture is slot based and provides for multiple re-configurable input/output (xe2x80x9cI/Oxe2x80x9d) connector modules (with integrated co-planar printed circuit boards (PCBs)) in the rear of the chassis which provide all external cable connections. It also provides for the majority of the active circuitry to reside on circuit modules which may be easily accessed and replaced from the front of the chassis. Internal connectivity is provided by a mid-plane or side-plane board which makes connection between the internal modules.
Within each slot, a three-dimensional envelope is defined within which the rear I/O connector modules may make a direct connection to the circuit modules. This provides great flexibility for each circuit module to connector module connection to be custom designed and hence optimized for each type of I/O to be supported. Within this envelope, a co-planar connection is made between the circuit module""s PCB and the PCB of the connector module to be used for electrical I/O signals. The connector module for electrical type signals then consists of a very simple single PCB with readily available right angle connectors on opposite edges, and a faceplate on the rear edge. Within this envelope optical I/O connections may also be made through fiber-optic connections on a connector module PCB or via a direct connection from a fiber-optic connector on the circuit module to a straight-thru fiber-optic adapter that is mounted on the rear faceplate. Again, the connector module remains quite simple, consisting of a smaller PCB for electrical connections and a simple off-the-shelf fiber-optic adapter mounted on the rear faceplate.
Each circuit module may be keyed directly to a corresponding mating connector module using a cylindrical plug and socket type key. The mating keying components reside on the PCBs of the circuit and connector modules and may pass through a hole in the mid-plane to mate with each other. The keying also aids in the alignment of the boards to one-another.
N+1 redundancy may be provided using ganged connector modules which occupy n+1 slots. These n+1 slot ganged connector modules are connected to one-another by an I/O inter-connection methodology that routes the n I/O signals to a slot containing a back-up circuit module. These ganged connector modules may be installed into the chassis as a single assembly with the I/O interconnection being an integral piece of it.